Magnetic material



May 15, 1928. 1,669,643

J. W. ANDREWS ET AL MAGNETIC MATERIAL Filed April 17, 1926 mien/0m Ja/mW ,44rd/ews fla/ydd/ 6////s Patented May 15, 1928.

UNITED STATES PATENT OFFICE.

JOHN WENDELL ANDREWS, OF CHICAGO, AND RANDALL GILLIS, OF BERWYN, ILLI-NOIS, ASSIGNORS T WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK,N. Y., A CORPORATION OF NEW YORK.

MAGNETIC MATERIAL.

Application filed April 17, 1926. Serial No. 102,729.

This invention relates to magnetic materials and magnet cores, and moreespecially to magnet cores for loading coils for telephone circuits andtheir method of produc- 6 tion.

The principal object of the invention is the production of a magneticelement having low core losses and a relatively high ermeability toenable a given inductance to 10 he obtained from a minimum amount ofmaterial, and possessing to a high degree those electrical and magneticcharacteristics which make it highly desirable in electrical signallingapparatus, particularly in loading coils for telephone circuits.

In accordance with one embodiment, the present invention contemplatesthe construction of magnet cores of an alloy including nickel and ironin finely divided form, heat treated to have a higher inherent'magneticpermeability and lower inherent hysteresis loss than iron, and combinedwith a suitable insulating material. More specifically, the inventioncontemplates the formation of the ma et cores of a nickel iron alloy infinely divided form in which the proportions of its constituents aremore than 25% of nickel and the remainder principally iron, and in aform which has proven satisfactory the nickel content beingapproximately 78 of the whole. The metal particles are treated with asolution of chromic acid in the presence of an alkali and a fillerWhereb the alloy particles are individually insu ated after which theyare compressed into cores of the desired shape and, size. The cores areheat treated at the optimum temperature for the particular alloy ofwhich the cores are constructed to stabilize the insulator and to give ahigh permeability and low hysteresis and eddy current losses.

It is believed that the invention will be clearly understood from thefollowing detailed description of one embodiment thereof and theaccompanying drawing, in which Fig. 1 is a perspective view of a sectionof a loading coil core made in accordance with the present invention,and

Fig. 2 shows a plurality of these sections assembled to form a completedcore.

It will be understood. however, that this is merely illustrative and theinvention is not limited to the production of this form of core, but isadapted to the production of REISSUED cores for magnetic articles ofmany forms.

in carrying out the present invention the magnetic material is preparedin the following manner. The'magnetic material employed is preferablypre ared from a nickel lron alloy commonly re erred to as permalloy,which is treated in a manner more fully described in the copendingapplication of C. P. Beath and H. M. E. Heinicke, Serial No. 101,179,filed April 10, 1926, to reduce the alloy to a finely divided form.Experience has proven that where low eddy current losses are desired itis essential that the particles be of a small size and preferably ofsuch size that all of the particles will readily pass through what isgenerally known as a one hundred and twent mesh screen and a. largepercentage pass through a. two hundred mesh screen. Ac'cordin to oneembodiment of the invention the a 0y is prepared by meltingapproximately 78 parts of nickel and 21 parts of iron in an oxidizingatmosphere and pouring the resulting alloy into a mold. When preparedaccording to the foregoing process the resulting alloy will beexceedingly brittle and is therefore particularly adapted to be reducedto a finely divided or dust form from which the finished cores aremolded.

After the brittle ingots are obtained they are successively passedthrough pro ressively reducing hot rolls which form t e alloy into fiatslabs approximately 4 thick. By the hot rolling process the size of thec stalline structure is materially reduced which since thedisintegration of the material takes place mainly at the crystalboundaries, is essential in order to have a satisfactory yield of dust.The rolled slabs are broken into short pieces and are then crushed in ajaw crusher, hammer mill or any other suitable type of apparatus inwhich a further reduction occurs. The material after being passedthrough the jaw crusher is subsequently,

rolled in a ball mill until it is reduced to a. fine dust. This dust issieved through a. one hundred and twenty mesh sieve and any residue isrenielted and the foregoing operation is again repeated to reduce thematerial to a finely divided form. Prior to the addition of theinsulating material the fine- 1y divided particles of the nickel ironalloy are annealed in a closed container at a temperature ofapproximately 750 C. to 980 C.,

a temperature of about 925 C. having proven to be one which producesvery satisfactory results. It is then necessary to again reduce theannealed alloy which is now in the form of a cake, to a finely dividedform after which itis mixed with the insulator.

According to one form of the invention, the insulator for the dustparticles isprepared by mixing the ingredients in approximately thefollowing proportions:

5 parts of chromic acid, 5 parts of talc, 4 parts of water glasscomposed of 50% total solids and containing approximately 1.58 parts ofSiO. to 1 part of Na O. Suflicient water is added to the ingredients tomake a rather dilute solution. This solution is thoroughly mixed and thepermalloy particles added to the solution, the amount of the permalloyparticles added being determined by the permeability desired and theparticular use to which the finished cores are to be put. The entiremass is then boiled to dryness, accompanied by constant stirring toprevent caking and to insure a thorough coating of the individual dustparticles, but it is not heated to such a degree of dryness that thechromic acid loses its adhesive properties. The dried insulated dustparticles are then in a form suitable for pressing into cores or ringswhich are preferably formed with a pressure of approximatel 200,000pounds per square inch. A big pressure is used in forming the rings inorder to increase their density, since it has been found that thepermeability of the rings increases with increased density. Followingthis Step in the process of constructing the cores and without undulyexposing them to the air they are transferred to an annealing furnace inwhich they are annealed at the optimum annealing temperature ofapproximately 500 C. and cooled. In order to make the cores chemicallystable and to remove all soluble substances such as chromates the coresare boiled in water until a solution obtained by boiling a crushed testring in water will show only a trace of soluble chromates when testedwith silver nitrate. After this operation the cores or rings are driedat a temperature of approximately 100 C. A few test rings may be made ofdust insulated in the above manner and their permeability measured.Should their permeability be too low, it may be increased" by theaddition of a predetermined quantity of uninsulated dust to theinsulated dustbefore it is pressed into rings.

A plurality of rings thus formed are then stacked coaxially to form acore on which the usual toroidal winding is applied, the number of suchrings used depending upon the existing electrical characteristics of thetelephone circuit with which the loading coils are to be associated.

Although the permalloy particles have been described as being insulatedwith a solution of chromic acid, water lass and talc in definiteproportions, it is 0 course to be understood that the proportions of thedifferent ingredients may be varied without departing from the spiritand scope of the invention. Also chromic acid alone may be used as theinsulator in such cases where mechanical strength is not an essentialcharacteristic of the finished cores. Then, too, other acids thanchromic may be used with satisfactory results, among these beingmolybdic, tungstic, antimonous and phosphoric acids, and the water glassand talc may be likewise re laced with other alkalies, such as sodium hyroxide and sodium aluminate and fillers such as zinc oxide, aluminumoxide and barium oxide and still produce magnet cores which aresatisfactory from both an electrical and magnetic standpoint.

By using an alloy of the proportions stated in the preceding paragraphsand by following the foregoing method of insulating the individual alloyparticles and compressing the particles into cores or rings, magnetcores or rings are produced which have an extremely high permeabilitywith aminimum amount of material employed. By the use of such cores orrings, inductance units having the same ermeability with equal or lesshysteresis ant eddy current losses as cores constructed according topreviously known methods, but with much less core volume and much lesscoil volume, are availble.

What is claimed is:

1. As a new article of manufacture, a magnetic substance composed ofparticles of loo a magnetic material, and an insulating materialconsisting of chromic acid, an alkali, and a filler separating theparticles.

As a new article of manufacture, a magnetic substance composed ofparticles of a magnetic alloy of nickel and iron, and an insulatingmaterial consisting of chromic acid, an alkali, and a filler separatingthe particles. Y

3. As a new article of manufacture, a magnetic substance composed offinely divided particles of a magnetic alloy of nickel and iron, and aninsulatingmaterial consisting of chromic acid, water glass, and a fillerseparating the particles.

4. As a new article of manufacture, a magnetic substance composed offinely divided particles of a magnetic alloy of nickel and iron, and aninsulating material consisting of chromic acid, an alkali, and talcseparating the particles.

5. As a new article of manufacture, a mag-' netic substance composed offinely divided particles of a ma netic alloy of nickel and iron, and aninsu ating material consisting of chromic acid, water glass, and talcseparating the particles.

6. As a new article of manufacture, a

magnetic substance composed of finely divided particles of a ma eticalloy of nickel and iron, and aninsu ating material consisting of partschromic acid, 4 parts water glass, and 5 parts talc separating theparticles.

7. As a new article of manufacture, a magnetic substance composed offinely divided particles of a magnetic alloy com-' posed of more thannickel and the remainder principally iron, and an insulating tures,which consists in coating particles of a magnetic material with aninsulating material, consistin of chromic acid, an alkali and a filler,an forming a mass of such insulated particles into a homogeneous solid.

10. The method of making magnetic structures composed of an alloy, whichconsists in reducing the allot; to a finely divided form, heat treatingt e finely divided particles, reducing the product so obtained to afinely divided form, coating the resulting product with an insulatingmaterial comprising chromic acid, and forming a mass of such insulatedparticles into a homogeneous structure.

11. The method of making'magnetic structures composed of an alloy, whichconsists form, heat treating t e finely divided arto a finely dividedform, coating the resulting in reducing 'the allo to a finely div'gdedproduct with an insulatin material comprising chromic acid, an alkaliand a filler, and forming a mass of such insulated particles into. ahomogeneous structure.

12. The method of making magnetic structures composed of an alloy, whichconsists in reducing the alloy to a finely divided form, heat treatingthe finely divided par-; ticles, reducing the product so obtained to afinely divided form, coating the resulting product with an insulatingmaterial comprising chromic acid, forming a mass of such insulatedparticles into a homogeneous struc ture, and heating the structure to ahigh temperature.

13. The method. of making magnetic structures composed of an alloy ofmore than 25% nickel and the remainder principally iron, which consistsin reducing the alloy to a finely divided form, heat treating the finelydivided particles, reducing the'product so obtained to a finely dividedform, coating the resulting product with an insulatin materialc'omprlsing 5 part s chromic aci 4 parts water glass and 5 parts'talc,and forming a mass of such insulated particles, into a homogeneousstructure.

14. The method of making magnetic structures composed'ot an alloy ofmore than 25% nickel and the remainder principally iron, which consistsin reducing the alloy to a finely divided form, heat treating the finelydivided particles, reducin the product so obtained to a finely dividedorm, coating the resulting product with an insulating materialcomprising 5 arts chromic acid, 4 parts water glass an 5 parts talc,formin a mass of such insulated particles into a iomogeneous structure,and heating the structure at a high temperature.

15. The method of producing a magnetic structure, which consists inmixin magnetic dust with an insulatin materia forming a mass of theinsulate dust into a homogeneous solid, and subjecting said solid to aheat treatment at an optimum temperaiure determined by the point ofminimum oss. a v

16. The method of producing a magnetic structure, which consists inmixing ma etic dust with an insulating material, forming a mass. of theinsulated dust into a homogeneous solid, and heating'th'e solid to atemperature of approximately 500 C. I

17. The method of producing a magnetic structure, Which-consists inmixing magnetic dust with an insulatin material, including 100 an acidas an element orming a mass of the insulated dust into a homogeneoussolid, and heat treating the solid at an ptimum temperature determinedby the point of minimum loss. a

18. The method of producing a magnetic structure, which consists inmixing nickeliron particles with an insulating material, forming a massof the insulated dust into a homogenous solid, and subjecting said solid110 to a heat treatment at an optimum temperapure determined by thepoint of minimum 7 oss.

In witness whereof, we hereunto subscribe our names this 31st day ofMarch A. 1),, 115

JOHN WENDELL ANDREWS. RANDALL GILLIS.

